Many modern cellular devices can connect to packet-based networks over mobile access networks. For example, mobile telephones and other types of devices can connect to the Internet via a cellular radio access network. The service providers who operate such access networks may charge subscribers based on a variety of criteria, such as how much data the subscribers transfer over the access networks, the time of day the data is transferred, a service level for the subscriber and the like. For instance, a service provider may charge or bill a subscriber a given amount of money if the subscriber transfers more than a given amount of data over the access network in a billing period.